The purpose of these investigations is to isolate and identify the bacterium and host cell recognition sites specifically required for successful infection by Agrobacterium, and to determine the nature of this interaction, its role in tumor transformation, and the extent to which variations in pathogenicity and host range of different Agrobacterium strains are correlated with these differences. The biological activity of Agrobacterium cell envelope preparations will also be assessed alone and in combination with avirulent strains. The bacterial site-binding component will be isolated from A. tumefaciens strain B6 cell envelope preparations by standard techniques used in the study of gram-negative cell wall components, fractionated chromatographically and the presence of site binding material assayed by its ability to inhibit tumor formation on bean leaves by competing with virulent bacteria for the host attachment site. Host site components will be isolated starting with cell wall and membrane preparations from susceptible bean leaves and purified by chromatographic procedures by following the ability of isolated site components to compete for bacteria with in vivo sites in the bean leaf infectivity bioassay. The sites from strains of Agrobacterium showing differences in virulence, host range, and symptom formation, and from resistant and susceptible hosts will be prepared. BIBLIOGRAPHIC REFERENCES: Whatley, M.H., J.S. Bodwin, B.B. Lippincott and J.A. Lippincott. 1976. Role for Agrobacterium cell envelope lipopolysaccharide in infection site attachment. Infect. Immun. 13:1080-1083. Spiess, L.D., B.B. Lippincott and J.A. Lippincott. 1976. The requirement of physical contact for moss gametophore induction by Agrobacterium tumefaciens. Amer. J. Bot. 63: 324-328.